The present invention relates to a thin film of aluminum alloy, a sputtering target material for forming a thin film of aluminum alloy, and a method for forming a thin film of aluminum alloy. More particularly, the invention relates to a thin film of aluminum alloy which is endowed with high heat resistance and low electric resistance and which is used for forming thin film wiring for liquid crystal displays, electrodes, wiring of semiconductor integrated circuits, and similar purposes; a sputtering target material for forming of such aluminum alloy thin film; and a method of forming such aluminum alloy thin film.
In recent years, liquid crystal displays used in display units of computers and in notebook-type personal computers have come to be larger in size and possess a higher resolution. Recently, in the field of liquid crystal displays, there has been an increasing demand for thin film transistor (TFT) liquid crystal displays, and to keep pace with this trend, they are required to have better characteristics. Particularly, the greater the dimension and the higher the resolution of liquid crystal display devices, the lower the specific resistance (10 xcexcxcexa9xc2x7cm or lower) the wiring material is required to have. This demand stems from the necessity of preventing signal delays arising from the formation of long, fine wiring.
Hitherto, high-melting-point materials such as Ta, Cr, Ti, and alloys thereof have been employed as wiring materials for fabricating liquid crystal displays. However, since these high-melting-point materials have an excessively high specific resistance, limitations have been imposed on use thereof in the wiring of the aforementioned wide-dimension and high-resolution liquid crystal displays.
Under such circumstances, elemental aluminum has become of interest as a wiring material due to its very low specific resistancexe2x80x94as low as approximately 3 xcexcxcexa9xc2x7cmxe2x80x94and high ease of handling in wiring. However, elemental aluminumxe2x80x94having a relatively low melting point of 600xc2x0 C.xe2x80x94exhibits disadvantageously low heat resistance.
After aluminum thin film is formed on a substrate through sputtering and the thus-formed thin film is processed to thereby form wiring, insulating film is formed on the wiring through CVD. During the CVD process, the aluminum wiring is heated to 300-400xc2x0 C. During heating, nodular bumps called xe2x80x9chillocksxe2x80x9d are generated on the surface of the aluminum thin film. These hillocks penetrate the insulating layer, thereby causing a short circuit with the adjacent upper layer, or between layers adjacent to one another, leading to failures.
In order to solve the above problem, a number of companies have developed aluminum alloys to which another alloying element has been added, and the resultant alloys have come to be used widely. Such alloying is known to prevent the generation of hillocks to a considerable degree. Regarding thin film of an aluminum alloy such as Alxe2x80x94Ti, which has heretofore been employed, hillock generation is certainly prevented by controlling the amount of an added alloying element such as Ti.
However, addition of another alloying element to an aluminum alloy also elevates the specific resistance to higher than 10 xcexcxcexa9xc2x7cm. Species and amounts of additional elements greatly affect the characteristics of aluminum alloy thin film. Thus, it is desired to produce an aluminum alloy thin film which has a low electric resistance and a high heat resistance and in which hillock generation is prevented.
Thus, an object of the present invention is to provide aluminum alloy thin film which is endowed with heat resistance and low electric resistance, even after being subjected to heat treatment at 300-400xc2x0 C., which prevents generation of hillocks, and which has a specific resistance of 7 xcexcxcexa9xc2x7cm or less. Another object of the present invention is to provide a sputtering target material employed for forming the aforementioned aluminum alloy thin film. Still another object of the present invention is to provide a method for forming the aforementioned aluminum alloy thin film.
The present inventors have conducted extensive studies so as to solve the aforementioned problems, and have found the following:
when the alloy composition of aluminum alloy thin film is of the Alxe2x80x94Cxe2x80x94Mg-base and the carbon content and the magnesium content is controlled to fall within predetermined ranges, the aforementioned problems can be solved;
when a sputtering target material is formed of an Alxe2x80x94Cxe2x80x94Mg alloy having a predetermined composition, the aforementioned problems can be solved; and
when the substrate temperature is controlled to, preferably, a predetermined temperature during formation of aluminum alloy thin film through sputtering, the aforementioned problems can be solved. The present invention has been accomplished on the basis of these findings.
Accordingly, the present invention provides a thin film of aluminum alloy, comprising, as components of the alloy, aluminum, carbon, and magnesium, characterized in that the carbon content and the magnesium content fall within a region defined by the following formulas:
X=0.61;
X=8;
Y=2;
and
Y=xe2x88x920.13X+1.3,
wherein Y (at %) represents the carbon content by atomic percent and X (at %) represents the magnesium content by atomic percent, and the balance of (X+Y) comprises aluminum and unavoidable impurities.
The present invention also provides a sputtering target material for forming thin film of aluminum alloy, comprising, as components of the material, aluminum, carbon, magnesium, and unavoidable impurities, characterized in that the carbon content and the magnesium content fall within a region defined by the following formulas:
X=0.61;
X=8;
Y=2;
and
Y=xe2x88x920.13X+1.3,
wherein Y (at %) represents the carbon content by atomic percent and X (at %) represents the magnesium content by atomic percent, and the balance of (X+Y) comprises aluminum and unavoidable impurities.
The present invention further provides a method for forming a thin film of aluminum alloy, comprising sputtering the aforementioned sputtering target material, to thereby form the aforementioned thin film of aluminum alloy, wherein the substrate temperature is maintained at 180-400xc2x0 C. during sputtering.